Common colds are the most frequent source of otitis media. When a child has a cold, fluid may build up behind the eardrum. This fluid creates a breeding ground for bacteria and viruses that lead to ear infections. As pus builds up and pressures the eardrum, the child experiences significant pain. Allergies can also trigger the congestion, fluid buildup and swelling of the eustachian tube that lead to an ear infection.  

Children are at higher risk for ear infections than adults because their eustachian tubes are shorter and narrower, their adenoids (gland-like structures located in the back of the upper throat) are large enough to sometimes hamper the opening of their eustachian tubes, and their immune systems are not fully developed.

Boys are at greater risk for ear infections than girls. Children with a family history of ear infections also appear to be more susceptible to these conditions. Other risk factors include:

• Chronic respiratory diseases such as asthma and cystic fibrosis
  
  

• Facial or brain abnormalities such as cleft palate or Down syndrome

• Impaired immune system, such as from chronic disorders like diabetes
  
  
• Attending daycare or other type of childcare facility
  
  
• Having siblings who often experience ear infections
  
  
• Exposure to second-hand smoke
  
  
• Upper respiratory tract infections such as a cold, strep throat or tonsillitis
  

External ear infections (otitis externa) result when normal ear bacteria and fungi overgrow as a result of exposure to moisture. Inner ear infections typically result from viruses – such as those responsible for measles, mumps or influenza – that spread from the middle ear to the inner ear. Bacterial infections of the inner ear are often the result of a spreading middle-ear infection or the spread of meningitis (an inflammation of the protective covering of the brain and spinal cord) into the inner ear. However, in many cases acute otitis media is caused by both bacteria and viruses.

In addition, a new study has found that children who suffer from chronic otitis media have bacterial biofilms on the middle ear tissue. Biofilms are antibiotic-resistant colonizations of bacteria that attach to surfaces and form a strong barrier that effectively prevents the bacteria’s destruction. Therefore, although antibiotics are effective for children with acute otitis media – where biofilms have not yet formed – those with persistent ear infections generally will not benefit from use of the medication.